The plant is a prodigious breeder, doubling its mass every two weeks. Its leaves starve the water of sunlight and cut off access to oxygen, which suffocates fish and encourages blooms of deadly green algae.

The hyacinth was virtually eliminated from East Africa's waterways in the 1990s. But now increased pollution has allowed the fast-growing plant to return.

Agricultural runoff and sewage both dump excess nutrients in the water that further the plant's spread.

Rain loaded with nitrogen from the smoke of countless wood cooking fires also pours into the lake, feeding the scourge.

"If this continues, the boats won't be able to land at all," said Okecho, leader of Kayago, a tiny fishing village near Lake Kyoga.

"Without fish, we won't have a shilling left. Kayago would dry up."

"Planting" Weevils

A native of South America, water hyacinth was introduced into Africa in the late 1800s.